Molecular Basis of Automaticity in the Myometrium

描述（由申请人提供）：早产（PTB），在妊娠第37周之前，显著增加长期并发症的风险，如神经发育障碍，智力迟钝，脑瘫，失明，耳聋和呼吸系统疾病，以及沟通和行为困难。虽然一些风险因素是已知的，但30 - 50%的自发性PTB的病因不明。子宫收缩，像所有平滑肌收缩一样，主要是机电事件，即，电信号引发收缩。虽然激素和生化途径在分娩条件的发展中起着关键作用，但子宫兴奋-收缩偶联的速度和协调表明，分娩中兴奋的短期协调信号是由离子通道携带的。妊娠期间子宫肌层电行为的改变一定是由起作用的离子通道的表达水平或行为的变化引起的。因此，自发性PTB反映了子宫电活动发展的异常时间。分娩期间的收缩是子宫肌层固有的节律性电活动（起搏）的结果。兴奋-收缩偶联的基本成分之一是起始去极化，即，"起搏器"电流。这个提议是基于我对子宫起搏电流的潜在分子基础的发现。我的初步数据显示，在子宫中有一类独特的离子通道，超极化激活的环核苷酸敏感（HCN）阳离子非选择性通道。在其他组织中，这些通道设置静息电位并产生节律性放电活动，即，与起搏和自动性有关。我的初步数据显示，相对于非妊娠子宫肌层，妊娠晚期HCN 1 mRNA表达上调约150倍，HCN 4转录下调约50倍。HCN 1通道激活速度比HCN 4通道快约10倍，在去极化电位约30 mV时激活，表明妊娠晚期HCN介导的自发电活动显著增加。这种与妊娠相关的HCN通道亚型（最容易和快速激活）（HCN 1）的显著上调被假设为导致自发子宫肌层兴奋增加，从而导致收缩。我的假设是HCN 1 mRNA的上调有助于妊娠子宫的起搏。该建议的目的是从分子水平鉴定子宫肌层中HCN通道亚型，并对相应的细胞电流进行电生理学鉴定和表征。早产导致巨大的医疗、社会、情感和经济成本。目前，还没有有效的方法来预防早产。确定子宫起搏器的离子通道为设计预防和延迟早产的干预措施提供了机会。早产导致巨大的医疗、社会、情感和经济成本。目前，还没有有效的方法来预防早产。确定子宫起搏器的离子通道为设计预防和延迟早产的干预措施提供了机会。

DESCRIPTION (provided by applicant): Preterm birth (PTB), prior to the 37th week of gestation, significantly increases the risk of long-term complications such as neurodevelopmental disabilities, mental retardation, cerebral palsy, blindness, deafness and respiratory diseases, as well as communication and behavioral difficulties. Although some risk factors are known, 30-50% of spontaneous PTBs have an unknown etiology. Uterine contraction, like all smooth muscle contraction, is primarily an electromechanical event, i.e., an electrical signal initiates contraction. Although hormonal and biochemical pathways play key roles in developing parturition conditions, the speed and co-ordination of uterine excitation-contraction coupling indicates that the short-term coordinating signals for excitation in labor are carried by ion channels. The alteration of the electrical behavior of the myometrium during gestation must arise from changes in the expression level or behavior of the contributing ion channels. Spontaneous PTB therefore reflects abnormal timing in the development of the electrical activity of the uterus. Contraction during parturition results from rhythmic electrical activity (pacemaking) intrinsic to myometrium. One of the fundamental components of excitation-contraction coupling is the initiating depolarization, i.e., the "pacemaker" current. This proposal is based on my findings of a potential molecular basis for a uterine pacemaker current. My preliminary data show a unique class of ion channels, Hyperpolarization-activated Cyclic Nucleotide-sensitive (HCN) Cation Non-selective channels, in the uterus. In other tissues, these channels set the resting potential and generate rhythmic firing activity, i.e., are involved in pacemaking and automaticity. My preliminary data show that HCN1 mRNA expression is upregulated ~150 fold and HCN4 transcript is downregulated ~50 fold in late gestation relative to non-pregnant myometrium. HCN1 channels activate ~10 fold faster and are activated at a potential ~ 30 mV more depolarized than HCN4 channels, suggesting a major increase in HCN-mediated spontaneous electrical activity in late gestation. This dramatic pregnancy related upregulation of the HCN channel isoform which is most easily and rapidly activated (HCN1), is hypothesized to result in increased spontaneous myometrial excitation and consequently contraction. My hypothesis is that the upregulation of HCN1 mRNA contributes to pacemaking in the pregnant uterus. The aim of this proposal is to molecularly identify HCN channel isoforms in the myometrium and to electrophysiologically identify and characterize the corresponding cellular currents. Preterm birth results in enormous medical, social, emotional and financial costs. Currently, there are no effective ways to prevent preterm birth. Identification of an ion channel which is the uterine pacemaker offers the opportunity for designing interventions to prevent and delay preterm labor. Preterm birth results in enormous medical, social, emotional and financial costs. Currently, there are no effective ways to prevent preterm birth. Identification of an ion channel which is the uterine pacemaker offers the opportunity for designing interventions to prevent and delay preterm labor.